1. Field of the Invention
This invention relates to an acetylene high polymer reinforced with a sheet-form product of a fibrous material, and to a process for preparing the reinforced acetylene high polymer. It also relates to a battery having the reinforced acetylene high polymer as at least one electrode.
2. Description of the Prior Art
It is known that a powdery acetylene high polymer prepared by polymerizing acetylene by using a so-called Ziegler-Natta catalyst comprising a transition metal compound and an organometallic compound exhibits an electrical conductivity falling within the semiconductor region and is therefore useful as an electrical and electronic element material. However, this polymer is not fused even if it is heated, and when the polymer is heated in the presence of oxygen, it readily undergoes oxidative deterioration, and cannot be molded according to conventional methods adopted for thermoplastic resins. Furthermore, a solvent capable of dissolving this acetylene high polymer has not been found. Accordingly, only the following two methods have heretofore been adopted for obtaining shaped articles of acetylene high polymers.
(A) A powdery low crystalline acetylene high polymer having no fibrous microcrystalline (fibril) structure is compression-molded by using a mold.
(B) Under specific polymerization conditions, polymerization is carried out to prepare a highly crystalline acetylene high polymer of a film form having a fibrous microcrystalline (fibril) structure (see Japances Examined Patent Publication No. 32,581/73).
Molded articles prepared by the above-mentioned method (A) have a low mechanical strength are difficult to use in many industrial fields. Molded articles prepared by the above-mentioned method (B) have a mechanical strength higher than that of the molded articles prepared by the method (A). However, the product of the method (B) does not have completely satisfactory mechanical strength.
It also is known that when this powdery low crystalline acetylene high polymer having no fibrous microcrystalline structure is treated with an electron acceptor such as BF.sub.3, BCl.sub.3, HCl, Cl.sub.2, SO.sub.2, NO.sub.2, HCN, O.sub.2 or NO, the electrical conductivity is increased by about 1,000 times, and in contrast, when this powdery acetylene polymer is treated with an electron donor such as ammonia or methylamine, the electrical conductivity is reduced to about 1/10,000 in the extreme case [D. J. Berets et al., Trans. Farady Soc., 64, 823 (1968)].
Furthermore, it is known that a highly crystalline acetylene high polymer having a lamellar structure is obtained under specific polymerization conditions [Makromol. Chem., Rapid Comm., 1, 621 (1980)]. It also is known that when a thin film of an acetylene high polymer prepared by the above-mentioned method (B) is chemically doped with an electron-accepting compound such as I.sub.2, Cl.sub.2, Br.sub.2, ICl, IBr, AsF.sub.5, SbF.sub.5 or PF.sub.6 or an electron donor such as Na, K or Li, the electrical conductivity of the acetylene high polymer can freely be controlled within a broad range of from 10.sup.-9 to 10.sup.3 .OMEGA..sup.-1 .multidot.cm.sup.-1 [J. C. S. Chem. Commu., 578 (1977), Phys. Rev. Lett., 39, 1098 (1977), J. Am. Chem. Soc., 100, 1013 (1978) and J. Chem. Phys., 69, 5098 (1978)]. It has already been proposed that this doped acetylene high polymer film, be used for the positive electrode of a primary battery [ Molecular Metals, NATO Conference Series, Series VI, 471-489 (1978)].
In addition to the above-mentioned chemical doping method, there has already been developed a method in which a p-type or n-type electrically conductive acetylene high polymer is prepared by electrochemically doping an acetylene high polymer with an anion such as ClO.sub.4.sup.-, PF.sub.6.sup.-, AsF.sub.6.sup.-, AsF.sub.4.sup.-, CF.sub.3 SO.sub.3.sup.- or BF.sub.4.sup.- or a cation such as R'.sub.4 N.sup.+ (R' stands for an alkyl group) [J.C.S. Chem. Commu., 1979, 594, C & EN Jan. 26, 39 (1981) and J.C.S. Chem. Commu., 1981, 317]. A re-chargeable secondary battery comprising an acetylene high polymer film obtained by the above-mentioned method (B), which is electrochemically doped, has been reported (Paper Presented at the International Conference on Low Dimensional Synthetic Metals, Hersinger, Denmark, Aug. 10-15, 1980). This battery comprises as positive and negative electrodes two acetylene high polymer films having a thickness of, for example, 0.1 mm, which are obtained by the method (B). When this battery is immersed in a tetrahydrofuran solution containing lithium iodide and is connected to a 9-V direct current power source, the acetylene high polymer film as the positive electrode is doped with iodine and the acetylene high polymer film as the negative electrode is doped with lithium. This electrolytic doping corresponds to the charging step. If a load is connected to the two doped electrodes, the lithium ion is reacted with the iodine ion and an electric power can be taken out. In this case, the open end voltage (Voc) is 2.8 V and the short circuit current density is 5 mA/cm.sup.2. When a tetrahydrofuran solution containing lithium perchlorate is used as the electrolyte, the open end voltage is 2.5 V and the short circuit current density is about 3 mA/cm.sup.2.
Since the above-mentioned battery is formed by using as the electrode material an acetylene high polymer which is capable of providing a light-weight and small-size battery, this battery is of interest as a cheap battery having a high energy density, the weight and size of which can easily be reduced. Each of the acetylene high polymers used for electrodes in these batteries disclosed in the prior art references is a porous acetylene high polymer film prepared by the above-mentioned method (B), and these batteries comprising electrodes formed of such acetylene high polymers are not satisfactorily sufficient in their cycle life, discharge voltage level and charging and discharging characteristics. Moreover, the electrodes prepared according to the conventional method have poor mechanical strengths and, in repeated charging-discharging test, polyacetylene is partially isolated from the electrode or the polyacetylene film is broken. Therefore, the application to batteries comprising as the electrode material of acetylene high polymers prepared by known methods is considerably limited and the development of a light-weight, small-size cheap battery excellent in the mechanical strengths of its electrode, the energy density and the discharge voltage level is eagerly desired in the art.
Some of the inventors of the present invention have already proposed several processes for preparing an acetylene high polymer having a fibrous microcrystalline (fibril) structure and having a higher mechanical strength, which processes are different from the above-mentioned conventional method, and also several methods for molding this acetylene high polymer (Japanese Unexamined Patent Publications Nos. 128,419/80, 129,404/80, 142,030/80, 145,710/80, 145,711/80 and No. 10,428/81), and also proposed new dopants for an acetylene high polymer (Japanese Unexamined Patent Publications Nos. 129,424/80, 129,425/80, 129,426/80, 129,427/80, 143,702/80 and 143,703/80).
However, when acetylene high polymers prepared by the known methods are used for certain purposes, for example, as electrode materials (J.C.S. Chem. Commu., 1979, 594), the mechanical strengths are not always satisfactory.